Stopping circuit for a high speed rotary switch



March 24, 1959 L. F. CRABTREE 2,879,339

STOPPING CIRCUIT FOR A HIGH SPEED ROTARY SWITCH Filed Sept. 12, 1956 F IG. 1

START SWITCH 20 I y V I T I I 'n- I IN VEN TOR.

LEONARD F. ORABTREE ATTY.

nited States Patent STOPPING CIRCUIT FOR A HIGH SPEED ROTARY SWITCH Leonard F. Crabtree, Downers Grove, Ill., assignor to General Telephone Laboratories, Incorporated, a corporation of Delaware Application September 12, 1956, Serial No. 609,372-

5 Claims. (Cl. 179-18) This invention relates to switch control circuits and more specifically to circuits for controlling the operation of high speed rotary stepping switches.

The object of this invention is to provide a stopping circuit for a stepping switch which circuit is capable of positively stopping the switch at a desired position regardless of the speed at which the switch is being operated.

A feature of my invention is a simplified switch control means requiring but a single standard tolerance relay as the main operating member.

Another feature of this invention consists of providing a simple test relay which locks out the switch operating circuit after the desired contact has been reached.

A further feature of the invention is the provision of the test relay functioning in connection with the bank contact immediately preceding the contact at which it is required that the switch be stopped so that the switch will cease its stepping when the required contact has been reached.

A further feature of the invention is in the added use of the flow of current for the operation of the test relay to slow the fiux breakdown in the switch motor magnet coil thereby prolonging the magnet release time and thus increasing the time in which the test relay is allowed to be energized.

At present there are many ways of stopping rotary switches operating either self-interruptedly or externally interrupted. Among these the most prominent and simplest is the absence-of-ground method. This consists of providing ground on each of the contacts of a level, but no ground is provided on the contact at which it is desired that the switch stop. The ground at each contact is used in any one of a number of ways to complete the operating path to the switch motor magnet. When the absence of ground appears on the open bank contact, the motor magnet receives no operating current and steps no further. This method is wholly adequate for low speed operation but is not positive enough a stopping arrangement for use in high speed applications. In high speed usages the wiper is too likely to skip on past the unmarked contact and hence continue stepping past the required stopping point.

For this reason most high speed applications require either relay stopping or combined relay and vacuum tube devices to stop the switch. With relay stopping, a test relay is usually connected to the wiper level, most frequently with a ground connection at the winding. Ground on the bank contacts as they are passed does not aifect the relay. At the required stopping contact, battery is connected and when the wiper passes over this contact, the test relay is energized and at its contacts opens the motor magnet operating path. The severe limitation imposed on this usage is that the stopping relay must be extremely fast operating in order to break the motor magnet operating path before the magnet is energized completely. To solve this problem a two-step relay haviugcritical adjustments is often employed. A more 2,879,339 Patented Mar. 24, 1959 thorough analysis of the stepping operation will show why these diificulties arise and those inherent in the two-step operation.

In an indirect drive switch operating self-interruptedly, when the motor magnet is energized this energy is stored in a driving spring and the magnet interrupter-contacts in its operate path are opened. The magnet then restores. As the magnet restores two things happen almost simultaneously. First, the interrupter-contacts fall back caus-' ing the magnet to be reenergized. Second, the switch steps to the next bank contact under the influence of the driving spring. As the wipers step onto the contact at which the switch is to be stopped, a battery pulse is fed from the marked bank contact to the stopping magnet thus energizing it. If the motor magnet thus becomes energized before a stopping relay connected to the same bank contact can pull up its contacts to open the magnet operate path, then the switch will continue to step. It is therefore necessary that the stopping relay must operate immediately, so that the motor magnet operate path can be opened before the motor magnet can fully pull up. At low speeds of switch operation, the stopping relay characteristics are not overly critical since the energization time of the magnets is low, however when self-interrupted high speeds of more than 50 steps per second are reached, then extremely fast-acting relays are a necessity. It can readily be seen that with more than 50 steps per second, a stopping relay must operate fully in but a few milliseconds to beat the motor magnet in operation. Relays to solve this problem must of necessity be critically made, adjusted and maintained at their optimum levels in order to function as required.

Lately, many circuits have been devised using combinations of vacuum tubes, resistors, condensers and relays. These naturally perform their task adequately with the many circuit components as stated.

The present invention allows the use in a stepping switch operating at the speeds mentioned, 50 steps per second or as fast as the switch can follow, of but a single relay as the main operating component of a stopping circuit. No critical adjustments or special functions are required of the relay and the circuit will operate properly under all conditions.

My invention insures that the switch will stop at a particular desired position at any operating speeds which can be attained by the use of a rotary stepping switch stepping either self or externally interrupted. The advantage of this simplicity for the positive control of fast switching is highly desirable in such fields as telephony, telegraphy, totalizers, computers and all other indus-' trial use.

It should be understood that only the test wiper and level have been shown. In practical usages naturally, the switch shown will have many additional wipers and levels providing control features for many external circuits. These features could consist of almost every industrial control usage and in telephone usage could be that of a rotary line finder stopping at the desired line. In a line finder usage, contacts 51 and 52 of Fig. 1 and contacts 51' and 52' of Fig. 2 would be suitable contacts on the line relay and or allotter to close on notice of a line to be found by this finder. Contacts 71 would be opened at the conclusion of this conversation to open the test relay holding path. Naturally this brief explanation is but one of the usages possible and the mentioned use would require a plurality of test circuits similarly constructed accessible to the bank contacts in a similar manner.

Fig. 1 shows the preferred embodiment of the current invention while Fig. 2 shows an alternative arrangement which may be used.

A high speed rotary switch which is adaptable for use 3 with the present invention is that shown in Patent No. 2,710,896 issued to K. W. Graybill and H. Sengebusch on June 14, 1955. Although this particular switch is referred to in the description and may readily be used with the present invention, this circuit may easily be applied to all types of stepping switches.

Fig. 1 shows contacts 51 and 52 which may be activated by any type of circuit component used to start the operation of the circuit, and can either manually or automatically be shut off and reset. Rotary switch 20 is shown having motor magnet 25, interrupter contacts 26 and a single non-bridging type bank Wiper 28 capable of resting on any one of bank contacts 31-30 as shown. Resistance-capacitance unit 40 is a standard one generally used for spark suppression and has no other major use in the circuit and its function is generally known. Test relay 10, a standard two-winding relay having an operate winding and a hold winding is shown with its contacts 11 and 12. The wiper 28 is shown resting on bank contact 31, an unmarked contact. Unmarked contacts may also have battery current connected thereon, the operation remains the same.

The operation of the circuit of Fig. 1 is as follows: Contacts 51 and 52 are closed in some manner as previously described. At contacts 51, the marking ground is connected through the operate winding of the test relay to contact 35, the marked contact. Contact 35 is marked with the previously described ground when it is required that the wiper 28 stop on the contact 36, the contact next following the marked contact 35.

On the closing of contacts 52, a circuit is completed from ground, through contacts 52, 12 and 26 to the winding of motor magnet 25 and battery. Motor magnet 25 is energized and then opens its own operate path at contacts 26. Magnet 25 then restores and wiper 28 steps under the effect of the switch driving spring to contact 32. When the motor magnet 25 releases, contacts 26 then reclose, magnet 25 reenergizes, opens its operate path again at contacts 26 and the switch steps wiper 28 to the next contact. This operation continues until contact 35 is reached. As the wiper steps from bank contact 34 to contact 35, magnet 25 has released, allowing its contacts 26 to drop back, thus closing its operate path once again. As the wiper 28 steps onto contact 35 a shunt is placed across the lower winding of relay 10 as follows: ground, contacts 51, relay 10, bank contact 35, wiper 28, contacts 26, 12 and 52, to ground. Relay 10 cannot operate. Magnet 25 is energized over its dual path consisting of its original operate path and another path to ground at contacts 51. As contacts 26 open due to this energization, the shunt across relay 10 is removed and this relay then operates. The resistance of the operate winding of relay 10 is suificiently high such that magnet 25 cannot remain operated over this path, but the operating current of relay 10 passing through the coil of magnet 25 will tend to slow the release of this motor magnet.

The period during which contacts 26 remain open is therefore of sufiicient duration to allow any standard relay such as relay 10 to operate since the allowable operate period begins when magnet 25 operates and ends when magnet 25 has fully released. Relay 10 is allowed enough time to energize and close its locking contacts 11 and open its contacts 12 in the magnet operate path. Magnet 25 restores and wiper 28 takes one step onto bank contact 36. Since relay 10 has locked itself operated over its upper winding and has opened the motor magnet operate path, wiper 28 continues to remain on contacts 36 until reset means 71 opens this relay hold path. Reset 71 may be any suitable means such as time delay relay contacts, reset button, cut-ofi relay or similar control mechanism.

By marking the bank contact immediately preceding the contact on which the switch is to stop, the invention utilizes the maximum allowable time which the stepping sequence will allow in order to operate test relay 10. Test relay 10 is allowed the complete open period of contacts 26 in which to operate. This period starts with the opening of contacts 26 and continues until the deenergization of magnet 25 has progressed enough to allow contacts 26 to close. With a switch stepping self-interruptedly at a rate of 50 steps per second, which speed is relatively common in high speed operation, this aforementioned period would last slightly longer than 10 milliseconds without the magnetic effect previously mentioned. With this residual magnetic effect, magnet 25 adopts slow-to-release characteristics. The relay operate period is also notshortened at all by the operation of wiper 28 reaching contact 35 as is the operate period' allowed a stopping relay in the usual prior art. In the prior art relay stopping, magnet 25 cannot be energized in point of time until after wiper 23 has been stepped due to the prior deenergization of motor magnet 25 further shortening the test relay operate time.

Fig. 2 shows an alternate embodiment of the invention placing the test relay on the wiper 28' and ground alone on contact 35'. The operation of the circuit is generally identical to that previously described, in that during the time that magnet 25 is energized, contacts 26' are open and a circuit is completed to ground at bank contacts 35. The operate path of the motor magnet 25' is again locked open and the switch Wiper 28' steps to contact 36' on restoration of magnet 25' and is locked there.

What I claim is:

1. In a stepping switch, a switch wiper having a plurality of bank contacts accessible thereto sequentially, a source of potential connected to one of said contacts, an electromagnet for stepping said wiper to the next sequential bank contact on deenergization of said magnet, means for stopping the stepping of said wiper at a specific contact, said means comprising a test relay, said test relay rendered effective on said wiper reaching said one contact to cause said electromagnet to be denergized to thereby step said wiper to said specific contact, said stop ping means thereafter maintaining said electromagnet in a deenergized state.

2. In a switch having a wiper, bank contacts accessible thereto and a self-interrupted electromagnet for stepping said wiper, said wiper stepping one time on each self-interrupted deenergization of said electromagnet, means for stopping said wiper on a specific contact comprising a test relay associated with another of said contacts, means for energizing said test relay when said other contact is reached by said wiper and said electromagnet i energized, means responsive to the energization of said relay for causing said electromagnet to be deenergized and thereafter maintaining said magnet deenergized, said wiper thereby being stepped into engagement with said specific contact, said stopping means thereafter retaining said wiper on said specific contact.

3. In a switch having a wiper, bank contacts accessible sequentially thereto, an electromagnet for causing said wiper to sequentially touch said contacts, means for alternately energizing and deenergizing said electromagnet, said electromagnet causing said wiper to step to another contact on each of said deenergizations, means for stopping said wiper on specific ones of said bank contacts, said means comprising a relay for each of said specific contacts, said wiper on reaching the contact prior sequentially to one of said specific contacts causing operation of the associated relay after said electromagnet has energized, means associated with said last relay and responsive thereto for causing said electromagnet to become deenergized and to thereby step said wiper one more step onto said one specific contact, means for locking said relay operated thereby causing said wiper to remain on said specific contact.

4. In a stepping switch having a wiper and a series of contacts with a magnet having means for stepping the wiper sequentially over said contacts upon each deenergization thereof, means for marking certain of said contacts, means for starting the operation of the switch to operate the wiper and cause it to test for a marked contact, a test relay having a circuit completed whenever a marked contact is engaged, said relay energized over said circuit simultaneously with the next energization of said magnet, and means controlled by the operation of said relay to open the circuit of said magnet and lock itself energized to thereby cause the wipers to he stepped to the next contact and prevent further operation thereof.

5. In a stepping switch having a wiper and bank contacts accessible thereto, an electromagnet causing said wiper to sequentially touch said contacts on each deenergization of said eleetromagnet, means for marking one of said contacts, a test relay operable on said wiper touching said marked contact and after said electromagnet has again energized, said relay having an operating path through said electromagnet, means associated with said relay for causing said electromagnet to be deenergized on operation of said relay, said relay through the medium of its operating path causing said electromagnet to be deenergized slowly, further means associated wtih said relay for causing said relay to lock operated, said wiper being stepped as a result of said last mentioned electromagnet deenergization, further means associated with said relay for causing said wiper to remain stationary after said last mentioned step.

References Cited in the file of this patent UNITED STATES PATENTS 2,682,019 Molnar June 22, 1954 

